National Republicans are excited about Sean Duffy, a Wisconsin district attorney and one-time “Real World” star who is attempting to unseat Rep. David Obey (D-WI). Duffy is raising money, nabbing mentions on conservative blogs and has earned attention on the National Republican Congressional Committee “young guns” list of potential stars.

But he’s got a tea party candidate, produce and dairy farmer Dan Mielke, labeling him as the establishment’s favorite at every turn.

Will this primary stop being polite?

The usual indicators of cash and organization suggest that Duffy will at least mount a serious challenge against Obey and the NRCC freely praises him despite not officially taking sides in GOP primaries.“Sean Duffy really is a top-tier, outstanding candidate who is getting the grassroots excited,” Tom Erickson, an NRCC spokesman who added that Duffy’s organization is strong.

Erickson said Duffy is showing “bravery” to take on the appropriations committee chairman. Obey has been in Congress 40 years.

Duffy “would appeal well to tea party voters,” Erickson said.

Mielke balks at that assessment, and says Duffy has “Hollywood” values and is too close to the establishment in Washington.

Mielke challenged Obey in 2008, and boasts he earned a higher percentage of the vote than any Republican has in decades against the powerful Democrat. But that percentage was just under 40 percent – a blowout by most standards even if it did happen in a presidential election year when Republicans were crushed nationally.

Mielke said the fight over immigration in 2006 and 2007 prompted him to get involved and run for office, and called Obey “socialist minded.”

“I’m more of a tea-party type candidate, I don’t cowtow to the leadership,” Mielke told TPMDC today in an interview. “He’s what I call the Republican puppet and I’m more the guy who came off the street.”

He accused Republican leaders of attempting to choose their preferred candidate in a “backroom” similar to what happened in New York’s 23rd Congressional district last fall that led to the surge of the Doug Hoffman candidacy as a conservative candidate.

The primary is Sept. 14 – a date Mielke had to look up during our interview.

Duffy told TPMDC in an interview today he thinks he can win over Blue Dog Democrats who have voted for Obey without a viable alternative, adding the conservative base is “incredibly motivated” thanks to the stimulus, cap and trade bill and the health care debate.

“People are upset and they are ready for change,” Duffy said.

“Dan likes to say that I’m the establishment candidate, but the truth is I have support from a wide swath of people and he isn’t getting any traction,” Duffy said.

Duffy, an Ashland County District Attorney since 2002, also is a three-time World Champion Lumberjack athlete, ESPN Outdoor Games analyst, according to his Web site. He appeared on MTV’s “Real World: Boston” in 1997.

Obey’s campaign hasn’t returned our calls. We’ll update if they get back to us.

Thanks to reader KS for tipping us off to this race we’ll be watching.